The present invention concerns a method and device for geometrically transforming a compressed digital image in a computer communication network.
It also concerns a method of transferring a compressed digital image over such a communication network with geometric transformation of the image.
Techniques of manipulating images stored in a compressed digital data file are known, and notably techniques of geometric transformation of images in their plane by rotations and symmetries, directly in a compressed form, without requiring decompression of the digital data file.
This manipulation of data in compressed form, and notably of digital images, is of great interest in the field of telecommunications, when images are transferred on a set of electronic appliances connected by a computer communication network.
Such is the case in particular when an image, stored in compressed form in the memory of a computer, is to be printed in an orientation different from that in which it is stored on the computer.
The manipulation of images in compressed form makes it possible to reduce the memory space required for the geometric transformation of the image and to accelerate its geometric transformation compared with a geometric transformation of the image in a decompressed form, without any loss of information in the image.
These techniques of manipulation of digital images in compressed form are notably very useful when the images, acquired and/or stored on an appliance, referred to as the source appliance, is to be transmitted in order to be displayed or printed by other appliances connected to the source appliance and to each other so as to form a computer communication network.
The aim of the present invention is to optimise the manipulation of an image in compressed form stored in a computer communication network.
Thus the present invention relates to a method for the geometric transformation of an image stored in a compressed digital data file, the said image being stored on a source appliance connected to one or more other appliances by a computer communication network.
This geometric transformation method is characterised in that it comprises the following steps:
choosing a set of appliances in the computer communication network adapted to implement a geometric transformation of an image in compressed form;
selecting an appliance in the said set in order to implement a geometric transformation of an image in compressed form;
transmitting the compressed digital data file to said selected appliance if it is different from the source appliance; and
geometrically transforming the image in compressed form by the selected appliance.
Correlatively, the present invention also relates to a device for the geometric transformation of an image stored in a compressed digital data file, said image being stored on a source appliance connected to one or more other appliances by a computer communication network, characterised in that it comprises:
means of choosing a set of appliances in the computer communication network adapted to implement a geometric transformation of an image in compressed form;
means of selecting an appliance in the said set in order to implement a geometric transformation of an image in compressed form;
means of transmitting the compressed digital data file to said selected appliance if it is different from the source appliance, in order to geometrically transform the image in compressed form by means of the selected appliance.
The choice of the appliance in the communication network is thus made on all the appliances able to implement a geometric transformation of the image in compressed form.
By virtue of the invention, the image in compressed form is manipulated by an appliance in the communication network, which can possibly be different from the source appliance.
According to a preferred version of the invention, at the selection step, a comparison is made, when the number of appliances in the said set is greater than one, between one or more criteria amongst the operating speed of the microprocessors in the appliance, the size of the available memory in the appliances, the number of users of the computer communication network using the appliances, the transmission rate over the communication network between appliances, the latency time in order to be able to transmit the file over communication links between the source appliance and the other appliances and the number of necessary transmissions of the file over the network in order to reach a receiving appliance, and the most effective appliance is selected according to the criterion or criteria.
Thus the present invention makes it possible to choose, when several appliances in the communication network are able to manipulate the image in compressed form, the most effective appliance according to criteria of speed of transmission, speed of processing and available space for effecting this processing.
The computing and processing capacities of an appliance must be compensated for by the transfer time required to transmit the file to this appliance via the communication network.
According to another preferred version of the invention, the choosing step includes the following substeps:
the selection of a group of appliances in the computer communication network comprising said source appliance and one or more appliances adapted to transmit information to the source appliance;
the reception by the said source appliance of information transmitted by the appliances in said group about the capability of said appliances of implementing a geometric transformation of an image in compressed form; and
the restriction of the group of appliances to said set of appliances in the computer communication network adapted to implement a geometric transformation of an image in compressed form.
Thus the inventory of the appliances in the communication network adapted to implement a manipulation in compressed form of the image is made at the level of the source appliance, amongst the group of appliances in the network having the capability of communicating information with the source appliance and notably of giving information about the manipulation techniques used by the appliances in this group and transmitting and receiving compressed digital data files.
According to a preferred version of the invention, which makes it possible to choose, at the level of the source appliance, the appliance in the network which will effect the manipulation of a compressed image, the device for the geometric transformation of an image is incorporated in this source appliance, storing said image in a compressed digital data file and connected to one or more appliances in a computer communication network.
According to an advantageous version of the invention, when the image is compressed in a digital data file by means of a coding method including at least one step of spectral decomposition into frequency sub-bands, the geometric transformation step uses a transcoding method applying a geometric transformation to symbols associated with the coefficients of the frequency sub-bands.
Thus the geometric transformation of the image can be effected directly on entropic codes or quantization symbols associated respectively with the coefficients of the frequency sub-bands obtained by spectral decomposition of the digital image, effecting, for example, at the very most an entropic decoding of the compressed digital data.
In a particularly advantageous aspect of the invention, a method of transferring an image stored in a compressed digital data file, between a source appliance and a receiving appliance in a computer communication network, is characterised in that it uses a method of geometric transformation of said image in accordance with the invention, and in that it also includes a step of transmitting the file of geometrically transformed compressed digital data to the said receiving appliance if it is different from said selected appliance.
Thus, when an image is transferred between a source appliance and a receiving appliance, requiring a geometric transformation of the image with a view to its processing via the receiving appliance, this manipulation in compressed form is effected in an optimum fashion on one of the appliances in the communication network, which may possibly be different from the source appliance and receiving appliance.
According to an advantageous version of the invention, allowing a particularly practical implementation of the invention, the device for the geometric transformation of an image is incorporated in a microprocessor, a read only memory containing a program for selecting an appliance in the network and transmitting the image to said appliance, and a random access memory containing registers adapted to record variables modified during the running of said program.
The invention also concerns a computer communication network characterised in that it has means for implementing the method of geometric transformation of an image or a device for the geometric transformation of an image according to the invention.
It also concerns a computer communication network characterised in that it has means for implementing the image transfer method according to the other aspect of the invention.
In a practical embodiment, the computer communication network has a source appliance storing the image in a compressed digital data file and a receiving appliance adapted to receive said image and to process said geometrically transformed image.
Preferably, the source appliance and/or the receiving appliance have means of implementing a geometric transformation of an image in compressed form.
Alternatively, or additionally, the communication network also has supplementary appliances having means of implementing a geometric transformation of an image in compressed form.
Advantageously, in a first embodiment for which the geometric transformation method is particularly well adapted, the source appliance is an appliance for acquiring a digital image, such as a computer, a scanner, a camera or a digital photographic appliance.
In a second embodiment, alternative or complementary to the previous one, the receiving appliance is an image display appliance, such as a computer or a digital television.
In a third embodiment, alternative or complementary to the first embodiment, the receiving appliance is an image printing appliance, such as a printer or a facsimile machine.
The present invention also concerns an information storage means, possibly partially or totally removable, which can be read by a computer or a microprocessor storing instructions of a computer program, characterised in that it is adapted to implement the method of geometric transformation of an image according to the invention.
It also concerns an information storage means, possibly partially or totally removable, which can be read by a computer or a microprocessor storing instructions of a computer program, characterised in that it is adapted to implement the image transfer method according to the invention.
The preferential or particular characteristics and the advantages of the geometric transformation device, of the communication network and of the aforementioned storage means are identical to those of the methods for the geometric transformation and transfer of an image according to the invention.